Willmeg,
Good point! Membership to the SyI is through a points system, points gained through experience, background and qualifications etc and presented to a board of validators who then decide at what level you can join. An MSc, BA or BSc will obviously stand you in good stead but not everyone can immediately embark on one of these academic courses for various reasons. I for one wanted some more academic experience before considering the higher level of postgraduate education. It just so happened that I accrued enough points through experience, education and courses to be validated as a full member. There is also the expense. A security related MSc could set you back upwards of £7000, so there is cost and some courses may not have the content you seek. As far as I am aware academic points can be taken into consideration for other similar subject related courses like an MSc. The BSc is just one such course you could consider, the fact that UofP have accredited it and tied it in to their BSc course shows that the Diploma has substance and crediblity. There is absolutely no pressure to continue your studies to another level. You may well be highly experienced and feel that a BSc will be of no benefit in the long run. Remember that around 75% of people in the security industry have no formal relevant security qualification - not that it is required of course, however more and more businesses and high end employers want high end qualifications. The SyI Diploma or the Certificate for that matter, could be a starting point or a finishing point for such academic recognition. Like any course, it gives academic experience and demonstrated capability.
I hope this helps and not hinders?